When a blood vessel is narrowed through plaque formation whereby fat is deposited or calcification or the like, the lumen of the blood vessel is expanded using a medical instrument called “stent” to secure blood circulation. For this stent, as other medical instruments, it is extremely important to evaluate the validity and safety thereof through an animal experiment or using an extracorporeal apparatus simulating a patient's lesion before applying it to the patient. However, there is no technique for creating any lesioned animal whose blood vessel is narrowed through calcification, and if such a technique exist, it may be extremely difficult to create an animal having such a lesioned blood vessel with a high degree of reproducibility. Furthermore, as a technique of creating a blood vessel model having a narrowed part, a method of producing a simulated blood vessel is disclosed in Patent Document 1. This producing method uses a core whose center part has a smaller diameter than other parts, fills a mold in which the core is accommodated with an aqueous solution of polyvinyl alcohol, casts the mold, repeats freezing and unfreezing, and then breaks and extracts the center part of the core, and can thereby create a simulated blood vessel made of polyvinyl alcohol hydrogel. Here, when injecting polyvinyl alcohol into the mold in order to form an adipose equivalent narrowed part, another aqueous solution of polyvinyl alcohol with lowered alcohol concentration is injected through a hole of the center part of the mold.    Patent Document 1: Japanese Patent Laid-Open No. 2004-275682